Also check your dncachesize, the DN cache tends to be the critical
element in back-hdb's performance. Still, if the filter attributes
are indexed it should not be so slow...

Wasn't aware of this parameter, and couldn't find it in the
administrator guide. Tried setting it to about the same as cachesize but
it doesn't seem to have a huge effect. The first time the search runs
after server-start-up, it still takes minutes to complete. Interestingly
enough, CPU usage is very low during this time, below 10%, and even
below 5% most of the time. iostat reports about 3.4% iowait.